Well, I haven't received any such email and my score in the class is 98% so far (with only the final exam pending this week).
I expected that around 10,000 people would have a perfect score in the class given my experience with Asian participation in online programming contests. There are a few countries in that part of the world where organizing a group to check each others' work and ensuring perfect scores is common and encouraged even when the official requirement is to do your own work. And those happen to be countries filled with millions of smart people. India, China, and Russia seem to be the heart of the phenomenon. Google, Facebook, and Topcoder have systems to deal with it but ai-class.org does not.
Anyway I'm neither surprised nor disappointed not to be in the top sliver. I'm not hireable anyway. It's funny that there is an identifiable top 1,000 at all instead of 10k+ perfect scores.
I'm not so sure about that given that I'm from one of the countries you've mentioned. My guess is that the profile of people who've taken part in ai class would be very different from what you would see in coding contest sites. Since no rewards were promised, I would think that those groups of people who would game the system to get perfect scores would be a very small number.